Create maze notebook (educational version)

Main features:
- the code is  sequential (ie one solver after one is tested)
- maze only related code (drawing, generation) put in a separate module
- implementation of our own rollout() to show how it works
- references to relevant articles for each solver + some brief
  explanation
- use of c++ A* (rather than python one) + euclidean distance as
  heuristic (easier to understand thatn manhattan distance)